The proposed research continues our collaborative genetic and biochemical attack on the identification, organization and function of mitochondrial genes of bakers' yeast, Saccharomyces cerevisiae. Attention is being devoted currently to the varl gene and flanking sequences. It is known that the sequences which determine varl protein size do not contain the complete structural gene, and may not contain any of the coding sequences. Thus, the structure or expression of this gene is novel. During this project period we will: (1) Complete the nucleotide sequence of the region of the mitochondrial genome which determines the size of the smallest allele of varl protein. In addition, we will determine sequences of alleles specifying larger varl proteins, and of the 3 mutants in varl function which have already been isolated. (2) Isolate and characterize additional varl mutants. (3) Purify chemical quantities of the varl protein from different alleles in order to determine regions of difference, and to carry out sufficient amino acid sequencing to help locate the varl structural gene. (4) Locate the transcriptional origin of the 16 S RNA which is complementary to the region of the genome which specifies the size of the varl protein, and determine whether any part of it contains translatable varl sequences. (5) Locate the complete structural gene for varl protein and determine its organization.